With the emergence and proliferation of wireless technology, the Internet today has evolved to a stage where numerous data communications end-points are made up of mobile terminals, each roaming through different domains and attaching itself to different points of attachment to a packet-switched data communications network (such as, the Internet) at different points in time. Such roaming provisioning is fairly matured in a circuit-switched communications network, such as the phone system. In a packet-switched communications network, however, supporting such roaming capabilities is difficult. This is because mobile terminals in a packet-switched communications network are reached using unique addresses, and such addresses usually contain portions (usually the prefix) that must be valid in a spatial topology. Also, it is desirable for mobile terminals to continue being reached at the same address after a plurality of change of point of attachment to the packet-switched data communications network. This allows seamless continuation of sessions (such as file transfer) across different points of attachment to the packet-switched data communications network.
To support such roaming capabilities, the industry has developed solutions for mobility support in Internet Protocol version 6 (IPv6). In mobile IP, each mobile node (i.e. mobile terminal) has a permanent home domain (i.e. a home network). When the mobile node is attached to its home network, it is assigned a permanent global address, known as a home-address. When the mobile node is away (that is, attached to some other foreign networks), it is usually assigned a temporary global address, known as a care-of-address. The idea of mobility support is that the mobile node can be reached at the home-address even when the mobile node is attached to other foreign networks, so that other nodes in the packet-switched data communications network need only identify the mobile node by the mobile node's home-address. Mobile nodes register their care-of-addresses with home agents using messages known as Binding Updates. The home agent is responsible for intercepting messages that are addressed to the mobile node's home-address, and forwarding the packet to the mobile node's care-of-address using IP-in-IP tunneling. IP-in-IP tunneling involves encapsulating an original IP packet in another IP packet. Such a binding between home-addresses and care-of-addresses, made known at the home agent of the mobile node, allows the mobile node to be reached no matter where the mobile node is. However, there exist a time when the mobile node has left a previous point of attachment and yet to set up a new binding between its home-address and new care-of-address (or even have not yet received a new care-of-address). During this time, no packet can be delivered to the mobile node.
In a conventional art, a method is disclosed to allow fast handoff between two base stations (see, for example, U.S. Pat. No. 6,473,413 B1 (October 2002)). In the disclosed method, when a mobile node roams to a new network, it issues a reassociation request to a base station A. In response to the reassociation request, the base station A finds the IP address of another base station B via a communications mechanism of mobile IP of IP layer, and then sends a handoff request frame to the base station B. In turn, upon receiving the handoff request, the base station B deletes the record of the mobile node in an association table, and then sends an handoff response frame back to the base station A via the communications mechanism of mobile IP. Then, a unicast handoff response frame will be forwarded to the base station A, and consequently the base station A can complete the handoff procedures.
In the above-described conventional method, however, the fast handoff requires base stations to actively participate, adding burden to the base stations' processing loads. Furthermore, the fast handoff procedures depend on the base stations capabilities (or offered functionalities). This makes the deployment of such method more complex, and often more expensive.
Existing solutions such as the above-described conventional method for supporting mobility in a packet-switched data communications network is inadequate in ensuring that a mobile terminal has a smooth, continuous communications session when in transit, because, although the method enables fast handoff between base stations, it still requires additions to base station functionalities. Not only does this increase the processing burden of the base station, it also requires special efforts to ensure compatibility between base stations from different vendors and service providers.
It is an object of the present invention to provide a mobile terminal apparatus and handoff method thereof which are capable of achieving smooth, continuous communications sessions even when in transit, regardless of base station capabilities and functionalities, in a packet-switched data communications network.
A mobile terminal apparatus according to one aspect of the present invention has: a plurality of interfaces each of which is capable of, when its associated access mechanism is in an active state, obtaining a connection to a network using either one of its home-address which is assigned in advance and its care-of-address which is assigned during its presence in a domain where its home-address is not available; an instructing section that instructs a setup of a binding of a home-address of a first interface, which loses a connection obtained using a care-of-address of said first interface, of said plurality of interfaces, and either one of a home-address and a care-of-address of a second interface of said plurality of interfaces, and a setup section that sets up said binding.
A handoff method according to another aspect of the present invention in a mobile terminal apparatus having a plurality of interfaces each of which is capable of, when its associated access mechanism is in an active state, obtaining a connection to a network using either one of its home-address which is assigned in advance and its care-of-address which is assigned during its presence in a domain where its home-address is not available, includes: an instructing step for instructing a setup of a binding of a home-address of a first interface, which loses a connection obtained using a care-of-address of said first interface, of said plurality of interfaces, and either one of a home-address and a care-of-address of a second interface of said plurality of interfaces; and a setup step for setting up said binding.